This invention relates generally to earth borehole apparatus, and specifically to caliper and centralizing apparatus having borehole wall-engaging faces urged against the borehole wall.
It is well known in the art of well logging to use caliper and centralizing instruments having a plurality of borehole wall-engaging members and having means, for example, a spring, to urge the borehole wall-engaging members against the borehole wall. For example, as discussed hereinafter with regard to the prior art, it has been known to use a bow spring interconnected between two rigid arms to contact the borehole walls. With such instruments, the bow spring generally has to have a large radius and the rigid arms have to be maintained at a low angle of approximately no greater than 20.degree. to 25.degree. to keep the connecting bow spring from overstressing the spring material. With such devices, there is generally a great distance between the pivot points on the rigid arms.
It is therefore a primary object of the present invention to provide a new and improved well bore instrument having means to centralize the instrument within the borehole;
It is also an object of the object invention to provide a new and improved well bore apparatus having means to caliper the earth borehole.
The objects of the present invention are accomplished, generally, by apparatus which includes an elongated support member adapted for movement through an earth borehole, at least one borehole-engaging member constructed to move along the wall of the borehole, means for coupling said at least one borehole-engaging member to said support member and adapted to urge said borehole-engaging member against the wall of the borehole and a bow spring attached to the coupling means and adapted to maintain the borehole-engaging member in contact with the borehole wall.